The effect of zeolite clinoptilolite (CLIN) on some metabolic parameters in blood serum and haematological values in weaned piglets fed with increased levels of zearalenone (ZEN) was investigated over a 14-day period. The research involved four groups of weaned piglets aged 40 to 54 days. All groups were fed on fodder mixture for growing pigs containing 20% crude protein and 12.57 MJ ME/kg. The first control group (C1) received a concentrate mixture without added ZEN or mycotoxin adsorbent Min-a-Zel Plus®. The second control group (C2) was fed on fodder mixture containing 0.2% of modified clinoptilolite (Min-a-Zel Plus®; levels of zearalenone <5.1 ng/g). Piglets in the experimental group (E1) were fed on fodder mixture containing added zeralenone (3 mg/kg) (Sigma-Aldrich Co) and 0.2% of Min-a-Zel Plus® preparation. The second experimental group (E2) was fed on fodder mixture to which 3 mg/kg of zearalenone was added, but with no addition of Min-a-Zel Plus®. Oestrogenic effect of ZEN was evident in the sinergistic action with insulin which was manifested in an increased total protein level, lower level of glucose, triacylglycerols, serum iron, a higer level of cholesterol and higher aminotransaminase activity. The metabolic antioestrogen effect of ZEN was established in group E2, whereas group E1 manifested the agonistic effect due to oestrogen reduction by clinoptilolite.